The list goes on. Republicans are tougher on their own than they are on their political opponents, and that just doesn’t make sense.

Do you see that coming from Democrats? You’re never supposed to say “never,” but it’s pretty darn close to never.

Look at what’s been happening to Hillary Clinton, the Democratic Party’s presidential candidate. She’s got more dirt on her than a West Virginia coal miner, but Democrats stay mum and don’t criticize her publicly over her email scandal, issues with the Clinton Foundation and her disconnect with the public about being an honest person. If you listened to Democrats talk about her, you’d think she’s Mother Theresa.

Can you think of one Democratic politician who’s gone public with complaints or concerns about Clinton ever since she won the party’s nomination? You’d be hard-pressed to come up with a name. They stay unified — and save their most critical comments for the opposition.

Where do we begin? The list is incredibly long. Let’s start with Mitt Romney, a fellow Republican, who ran against President Obama in 2012. Romney was roundly criticized for taking it easy on Obama during their campaign, but when it comes to The Donald, Romney is a bare-knuckled brawler. In an interview this summer, Romney said about a Trump presidency: ”I don’t want to see trickle-down racism. I don’t want to see a president of the United States saying things which change the character of the generations of Americans that are following.”

Speaker of the House Paul Ryan has publicly rebuked Trump over comments that he’s made about immigration. Cruz, of course, famously dodged endorsing Trump at the Republican convention.

A group of 50 senior national security officials, all alums of Republican presidential administrations, wrote a public letter warning that Trump would “risk our country’s national security and well-being.” All of the letter’s signatories said they will not vote for him.

Sen. Susan Collins (R-Maine) announced in a Washington Post op-ed that she will not vote for Trump, either. She’s the sixth GOP senator to take that stand.

This Republican mindset is not just about Trump, either. They squabble over who’s more conservative, who’s a moderate and who’s an “establishment” candidate. Democrats hardly ever have that type of public argument. They rarely characterize or scrutinize how liberal-minded their own candidates’ policies are (that is until Bernie Sanders arrived on the scene).

This Republican loathing is not just reserved for the party’s high-profile members. I’ve encountered local Republicans who get very aggressive when criticizing one of their party’s own candidates. Would they be this aggressive in attacking a Democrat? Probably not.

Truth be told, Republicans make themselves an easy target because they show great political courage in rebuking their own, but when it comes to confronting the opposition, they have a tendency to back off and appear weak-willed. They just don’t have the same feistiness or tenacity in taking on Democrats. Maybe that’s another reason why Trump makes so many Republicans feel uncomfortable. He’s a brawler. He won’t back down — from in-party attacks or from Democrats. For all his faults, that’s a trait that many Republicans probably secretly admire.

What Republicans have lost sight of is Ronald Reagan’s famous comment about criticizing a fellow Republican, the so-called “11th Commandment.”

To quote Reagan: “The personal attacks against me during the primary (when I ran for governor of California) finally became so heavy that the state Republican chairman, Gaylord Parkinson, postulated what he called the Eleventh Commandment: Thou shalt not speak ill of any fellow Republican. It’s a rule I followed during that campaign and have ever since.”

You know who practices the 11th Commandment? Democrats.

Indeed, Republicans have strayed mightily from Reagan’s political rule, and, as a result, it could end up costing them another presidential election in November.

Chris Stevens writes columns for the editorial page. Email him at stevens@mdn.net